Driver circuits are used in an integrated circuit to transmit signals. Driver circuits are commonly used to generate output signals at output ports of the integrated circuit. Because an output driver is coupled to a circuit such as a transmission line external to the integrated circuit, it is important that the circuit is matched to enable the signal to be properly transferred from the output port. In conventional series source termination (SST) driver configurations, a three terminal configuration, or T-coil, transformer has two ports connected to the driver output and the output port, and center tap port connected to an electro-static discharge (ESD) protection device. Accordingly, the T-coil is designed for the best return loss in the integrated circuit, and enables the transimpedance seen from the pads to be close to 50 Ohms at maximum bandwidth.
However, optimization of return loss does not necessarily optimize transient characteristics of the driver, such as rise and fall time, overshot, and settling time. Moreover, a three terminal transformer configuration generates a set of design parameters which need to be tweaked for fine tuning. These parameters include the inductances of two t-coil inductors L1 and L2, mutual coupling k between these inductors, resistances R1 and R2 of the inductors, and a bridge capacitance between two ports. Managing all these parameters together with port parasitic capacitance adds complexity to the design, and may not be critical for TX driver performance.